Sodium tellurite is an inorganic

tellurium Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

compound with formula Na₂TeO₃. It is a water-soluble white solid and a weak

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...

. Sodium tellurite is an intermediate in the extraction of the element, tellurium; it is a product obtained from anode slimes and is a precursor to tellurium.

Preparation

The main source of tellurium is from copper

anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...

slimes, which contain

precious metal Precious metals are rare, naturally occurring metallic chemical elements of high Value (economics), economic value. Precious metals, particularly the noble metals, are more corrosion resistant and less reactivity (chemistry), chemically reac ...

s as well as various tellurides. These slimes are roasted with

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

and oxygen to produce sodium tellurite. :Ag₂Te + Na₂CO₃ + O₂ → 2Ag + Na₂TeO₃ + CO₂ (400–500 °C) This is a reaction with silver telluride. The telluride is oxidized to tellurite and the silver(I) is reduced to silver.

Purification

The

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...

of a tellurite solution yields purified tellurium. :Anode: 4OH⁻ → 2H₂O + O₂ + 4e⁻ :Cathode: TeO₃²⁻ + 3H₂O + 4e⁻ → Te + 6OH⁻

Structure and properties

Tellurium has properties similar to sulfur and selenium. In the anhydrous form Na₂TeO₃ the tellurium atoms are 6 coordinate, three Te-O at 1.87 Å and three at 2.9 Å, with distorted octahedra sharing edges. In the pentahydrate, Na₂TeO₃.5H₂O there are discrete tellurite anions, TeO₃²⁻ which are pyramidal. The Te-O distance is 1.85 - 1.86 Å and the O-Te-O angle is close to 99.5°. The tellurite anion is a weak base. Sodium tellurite would be similar to sodium selenite and

sodium sulfite Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. It is also suitable for the softening of lignin in the pulping an ...

. Sodium tellurite is both a weak oxidizing agent and a weak reducing agent.

Tellurite-related reactions

:H₂TeO₃ → H⁺ + HTeO₃⁻ pK 2.48 Telluric acid loses a proton at this pKa. :HTeO₃⁻ → H⁺ + TeO₃²⁻ pK 7.7 Hydrogen tellurite loses a proton at this pKa to become the tellurite ion. This would happen in the reaction of tellurous acid with sodium hydroxide to make sodium tellurite. :TeO₂ + 2OH⁻ → TeO₃²⁻ + H₂O This is the reaction of tellurium dioxide with a base to make a tellurite salt.

Applications

Sodium tellurite improves the corrosion resistance of electroplated nickel layers. Solutions of sodium tellurite are used for black or blue-black coatings on iron, steel, aluminum, and copper. In microbiology, sodium tellurite can be added to the growth medium to isolate bacteria with an inherent physiological resistance to its toxicity.Borsetti, Francesca; Toninello, Antonio; Zannoni, Davide (2003). "Tellurite uptake by cells of the facultative phototroph Rhodobacter capsulatus is a pH-dependent process." Federation of European Biochemical Societies. Volume 554, Issue 3, 20 November 2003, pp. 315–318. Elsevier B.V.

References

*Cameo Chemicals. Sodium Tellurite. Retrieved March 8, 2009. Website: http://cameochemical.noaa.gov/chemical/5185. * {{Tellurites Tellurites Sodium compounds